Electrolytic cell for the production of aluminum

ABSTRACT

AN ELECTORLYIC CELL FOR THE PRODUCTION OF ALUMINUM COMPRISES A PLURALITY OF ANODES IN A SELF-COKING CAR BONACEDOUS ANODE MASS THAT IS PROGRESSIVELY LOWERED INTO THE BATH. THE ANODES HAVE FLATTNED UPPER ENDS WHOSE GREATEST WIDTH IS GREATER THAN THE WIDTH OF THE LOWER PORTIONS OF THE ANODES; AND THE ANODES ARE SUSPENDED BY CLAMPING THE NARROW EDGES OF THE FLATTENED UPPER ENDS. SO THAT THE ANODES CAN BE INSERTED AND REMOVED BY ROTATING THEM A QUARTER TURN ABOUT THEIR AXES. THE ANODES ARE ARRANGED IN SPECIAL PATTERNS RELATIVE TO EACH OTHER. THE ANODE MASS IS VERTICALLY MOVABLE BY A SPECIAL MECHANISM, AND IS ENCASED IN AN ALUMINUM SHEATH SECURED THERETO   WHICH IN TURN IS SURROUNDED BY AN INSULATING CASING OF SPECIAL CONSTRUCTION, WITH POWDERED ALUMINA FED DOWNWARDLY BETWEEN THE SHEATH AND THE CASING.

May 16, 1972 M. TOTH ET AL 3,663,419

ELEUTROLYIIC CELL FOR THE PRODUCTION OF ALUMINUM Filed Sept. 10, 1969 4 Sheets-Sheet l I 15 7L V 73 771 14 38\ j! i 27 Fig.2

INVENTORS M/H/Ily 70 777 (/5235: //1///PFF/ ATTORNEYS May 16, 1972 TOTH ET AL 3,663,419

I'JLIJCillOi/l'L'LU CELL FOR THE PRODUCTION OF ALUMLNUM Filed Sept. 10, 1969 4 Sheets-Sheet I3 F I94 INVENTORS BY rJZ L/N ATTORNEYS ELECIHOLYIIC CELL FOR THE PRODUCTION OF ALUMLNUM Filed Sept. 10, 1969 4 Sheets-Sheet S May 16, 1972 M. TQTH ETAL ELECIfiOLYIIC CELL FOR THE PRODUCTION OF ALUMLNUM Filed Sept. 10, 1969 4 Sheets-Sheet 4 INVENTIORS S a y W X m a; m. z 2 Ma United States Patent 3,663,419 ELECTROLYTIC CELL FOR THE PRODUCTION OF ALUMINUM Mihaly Toth and Jozsef Imrefii, Budapest, Hungary, as-

signors to Alutero Aluminiumipari Tervezo Vallatat,

Budapest, Hungary Filed Sept. 10, 1969, Ser. No. 856,533 Int. Cl. 301k 3/00; C2211 3/02; C23b 5/70 US. Cl. 204-225 12 Claims ABSTRACT OF THE DISCLOSURE An electrolytic cell for the production of aluminum comprises a plurality of anodes in a self-coking carbonaceous anode mass that is progressively lowered into the bath. The anodes have flattened upper ends whose greatest width is greater than the width of the lower portions of the anodes; and the anodes are suspended by clamping the narrow edges of these flattened upper ends, so that the anodes can be inserted and removed by rotating them a quarter turn about their axes. The anodes are arranged in special patterns relative to each other. The anode mass is vertically movable by a special mechanism, and is encased in an aluminum sheath secured thereto which in turn is surrounded by an insulating casing of special construction, with powdered alumina fed downwardly between the sheath and the casing.

The invention relates to electrolytic cells with selfcoking anodes with vertical current supply, as they are widely employed, for example, for the manufacture of aluminum by fusion electrolysis.

Because of problems arising in connection with power supply and temperature distribution, cells of large dimensions are constructed almost exclusively with periodically operating, prebaked block anodes with vertical current supply, or with self-coking anodes likewise provided with an upper current feed.

The presently known self-coking anodes in electrolytic cells with vertical current supply comprise a rigid anode sheath, the carbon anode proper, of the plug which is constantly coked during the operation, the bus bars, the anode mover, and the anode support structure.

The anode bar unit moves ever closer to the lower end of the anode and to the anode sheath during the operation of the electrolytic cell, due to consumption of the carbon anode. When this bar unit has approached *within about one to two feet of the upper part of the anode sheath, or has reached the lower dead center position determined by the anode mover, then the shifting of the anode bar unit is effected. Prior to this shifting operation, the upper ends of the anodes are temporarily affixed to the anode sheath; thereafter, the rigid connection between these ends, or current-conducting connecting pieces, and the anode sheath construction is released by opening the clamping device, and the anode bar unit is lifted into the upper position by means of the anode mover. Thereupon, the rigid connection between the ends which are already in the upper position and the anode bar unit is reestab lished and then the temporary mounting of the upper ends to the anode sheath is released. In the conventional cells, for the temporary aflixing of the anodes to the anode sheath, two supporting rods are disposed at the upper portion of the anode sheath construction between the rows of anodes or beside the outer row of anodes underneath the anode construction; these two supporting rods are an integral construction with the anode sheath or are designed to be portable.

In conventional cells, the anode bar unit consists of two cast aluminum or copper rails disposed above the "ice anode, or the cast bar is replaced by a pack of bars consisting of rolled plates which are joined to one another, or by a bundle of bars.

The anode bar units are connected at four points to the anode support construction with the interposition of the anode mover.

The disadvantages of the above-described electrolytic cells generally known in accordance with the present state of the art, with self-coking anodes having a vertical current supply, can be summarized as follows:

For given anode dimensions, the electric resistance and the heat loss of the anodes is high, and the slag formation is large. The geometric distribution of the heat losses or of the temperature of the anodes is disadvantageous in the cells known at present, so that it is impossible to further increase the dimensions of the cell in an economical manner. In the conventional constructions, the work involved in operating the anode, such as, for example, pulling the anodes, shifting the anode bar device, and supplying the anode with anode paste, is onerous. The required operations make it necessary to perform heavy physical or manual labor under working conditions which are very detrimental to health; on the other hand, when mechanizing the operating steps, such measures become very expensive in the case of conventional constructional designs. The solutions employed are very expensive and, consequently, the costs involved in placing such metallurgical plants on stream are especially high. Because of these disadvantages, the consumption of electrical energy involved in the manufacture of aluminum by means of such electrolytic cells is high; the costs of amortization and interest connected with the erection of the plants, per unit of production, are large; and the maintenance expenses are likewise substantial. Accordingly, the specific production costs are high, and it is difficult to 'procure operating personnel for conducting this unhealthy Work.

It is an object of this invention to eliminate the above disadvantages, particularly to reduce, for given cell dimensions, the electrical resistance and/or the heat loss and the investment costs, and to make feasible the economical utilization of cells having large dimensions.

Another object of the invention is to facilitate the operation of the cells and thus to lower the specific production costs, and/or to increase production.

The invention comprises an electrolytic cell for the manufacture of aluminum, including an anode bar, an anode support construction, an anode mover and advantageously with a self-coking anode with an upper end connector portion and a rigid inner jacket, wherein the electrolytic cell exhibits one or more of the characteristics enumerated below.

(A) The anode bar has a plurality of concave current transfer surfaces each of which lies on the surface of a cylinder with an essentially vertical generatrix, the axis of which cylinder is congruent with the axis of the anode upper end connector portion. However, the current transfer surface can also have other concave configurations or even be flat.

The upper ends of the anodes have at least one contact surface suitable for being electrically connected to the current transfer surfaces, formed along part of a convex surface of a cylinder with an essentially vertical generatrix, which contact surface may also be flat; and this upper end of the anode is fashioned so that any desired point of the contact surface is farther removed from the axis of the anode than any other surface points on the anode. The anode bus bar has one or more clamping elements suitable for the clamping, or for the electrical connection, of the contact surface of one or more anodes to the current transfer surface.

- (B) The anode assembly includes a metallic movable sheath, preferably of aluminum, attached to the anode mass or caked to the anode mass during operation; and/ or an outer rigid jacket having an internal contact surface which widens stepwise in the downward direction; and/or a layer of loose material between the carbon anode mass and the rigid jacket and made up of a granular or pulverized material, advantaageously alumina, fluorides, electrolytic carbon slag, coke dust, or mixtures of any of these in any desired ratio.

(C) The quotient of the total horizontal cross-sectional area of the anode mass and the number of individual anodes in the anode mass is, at most 0.23 mf preferably 0.05-0.15 m. The cell comprises advantageously at least three anode bars disposed in parallel with respect to one another and, connected to the sides thereof, preferably at least six rows of anodes.

(D) The anode mover has at least one element converting rotating motion into linear motion, preferably a screw element, more preferably a screw spindle having an axial motion. The axis of the rigid member executing the linear motion, or the center line thereof, is horizontal or forms an angle of, at most 45 with the horizontal. The anode bar unit comprises at least three suspension pulleys or sprockets; and the anode mover has at least three flexible power transmission elements, preferably wire cables or roller chains, one end of each of which is connected to the rigid member executing the linear motion, and the other end of which is connected, with the interposition of the suspension wheels, to the anode support unit or to the anode bar unit.

The individual aspects of the invention will be disclosed in greater detail with reference to the accompanying drawings showing examples of embodiments of the electrolytic cell of this invention.

FIG. 1 is a somewhat schemtaic view of the electrolytic cell of the invention in a vertical longitudinal section parallel to the rows of anodes. FIG. 1 also ShOWs an exemplary arrangement of the temporary anode support device of this invention disosed above the anodes;

FIG. 2 is a top plan view of FIG. 1;

FIGS. 3 and 4 show details of the anode bars of the electrolytic cell according to the invention. FIG. 3 illustrates part of a horizontal planar section through the anode bar along line BB of FIG. 4 with the anodes and the clamping elements, whereas FIG. 4- illustrates a section along line AA of FIG. 3;

FIGS. 5 and 6 illustrate an example of an arrangement of the anode supporting and anode moving devices, respectively, according to the invention, in an electrolytic cell having a regular hexagonal cross section. FIG. 5 shows an elevational view of the anode mover at right angles to the row of cells, and FIG. 6 shows a top plan view thereof;

FIGS. 7-9 show details of an exemplary construction of the anode sheath structure of this invention. FIG. 7 is a vertical section along line EE of FIG. 8, of the anode sheath construction at right angles with respect to the row of cells; FIG. 8 shows a horizontal section along line DD of FIG. 7, and FIG. 9 shows a vertical cross section along line FF of FIG. 7.

Referring now to the drawings in greater detail, and first to FIGS. 1 and 2, it will be seen that anode bar pairs are arranged in parallel with respect to one another and are disposed above a carbon anode mass of square cross section. These anode bars taper in cross section in the direction of current flow; and as can be seen from FIGS. 3 and 4, the current transfer surfaces 2 are formed on the anode bars 1 along the surfaces of hypothetical vertical cylinders that are coaxial with the upper ends 54 of anode stubs 22. The contact surfaces 3 of these ends 54 are adjacent to these current transfer surfaces, which contact surfaces are likewise formed along the surfaces of hypothetical vertical cylinders. Rigidifying elements 24 are disposed along the inner lateral surfaces of the anode bars 1. The height of elements 24 is greater than that of the anode bars 1. Anode guiding elements 25, in the form of plates, are connected by welding to the lower and upper edges of the elements 24. The guiding elements 25 have recesses 26 in the edges thereof, the outlines of which lie on circular arcs the centers of which are on the axes of the anodes. These recesses 26 determine generally the horizontal position of the anodes.

Each anode upper end has associated therewith respectively one spring steel support element 4 essentially parallel with respect to the anode bars 1. The anode ends 54 disposed on both sides of the current conducting members are staggered with respect to each other by onehalf the distance between the anodes, in the direction of the row of anodes.

Apertures 28 are provided on the anode bars 1 on both ends of the supporting elements 4; furthermore, corresponding openings 30 are formed in the bars 1 and elements 24. The apertures 28 and also the openings 30 are disposed essentially along a straight line at right angles to the bar 1, and a clamping bolt 5 is fitted through the aligned openings. -In one embodiment, the clamping bolt 5 is connected to the anode bar in a rigid or hinged fashion, preferably by nuts 31. In another embodiments, the clamping bolt 5 joins the elements 4 associated with diagonally adjacent anodes, so that the alternately connected clamping bolts 5 or elements 4 form a continuous series. The two ends of the series, i.e. the last two clamping bolts 5 or elements 4, are connected at their external ends to the anode bar 1. The clamping bolts 5 are fitted, with play, through the aperture 28 and the corresponding openings 30. A thread is provided on both ends of the clamping bolts 5 and at the point of emergence from the anode bar 1. At both ends of the clamping bolts 5, threaded nuts 29 are arranged which control the tilting of the series, and the threaded nut 31 is disposed on the screw thread provided on the inner part of the clamping bolts 5. The tilting control nut 29 serves for adjusting the optimum compressive force, or for regulating the tilting of the elements 4. With the aid of threaded nuts 31, the axial displacement of the clamping bolts in the corresponding openings 30 can be prevented. With the aid of the threaded nuts 31, the series (-5, 4, 5, 4, etc.) can be subdivided into several sections which can be adjusted independently of one another. At the level of the contact surface 3, the cross sectional configuration of the anode end 54 at right angles to the anode axis is a circular segment with two axes of symmetry, or a rectangle, or an elliptical-type planar configuration.

In operation, the contact surface 3 and the current transfer surface 2 are connected to each other. In this case, the elements 4 are in an elastically deformed, tensioned condition and thus press together the contact surface 3 to the current transfer surface 2. The flat sides 55 of the anode end 54 extend substantially at right angles to the current-conducting unit. If the end 54 is rotated about its axis by the fiat sides 55 are brought into a position which is substantially parallel with respect to the element 4 of the current-conducting unit. The element 4 and therebythe entire series 5, 4, 5, 4, etc. then become loosened. In this condition, the rotated anode can be pulled out toward the top in the direction of its axis. The element 4 associated with the rotated or pulled-out anode ensures that the two adjacent clamping bolts 5 are displaced in the direction of their axes with respect to the other side of the current-conducting unit. This makes it possible for the elements 4 adjoining the above-mentioned clamping bolts 5 and pertaining to the anode on the other side of the current-conducting unit to tilt. By the tilting of these supporting elements, the elastic deformation thereof decreases, and the compressive force likewise decreases. This released condition means an interruption of the electrical contact only in connection with the rotated anode. The remaining anode ends continue to be in contact with the current-conducting anode bar 1. However,

this contact is not as intimate as in the tensioned condition of the series. However, the amount of loosening is suflicient to permit extraction of the anode in question.

At the lower end of the anode ends 54, the current transfer section of the anodes 21 is provided, and thereabove the tapered section or stud 22 is formed. The diameter of this tapered section is greater than the diameter of the current transfer section of anodes 21. This makes it possible to remove an individual anode from the anode mass by raising it only a short distance and then swinging it over to the side. The length of the current-transferring section of anode 21 is advantageously 0.15-0.40 m. and is of cylindrical shape or is an inverted truncated cone of a conicity of at most 1%. The hole-widening section or stub 22 is an inverted truncated cone of a conicity of 1.53%. The lower diameter of the hole-widening tapered section 22 is 1.2 to 3 times, advantageously 1.2 to 1.5 times, the upper diameter of the current transfer section of anode 21. The current transfer section of anode 21 and the hole-widening tapered section or stub 22 follow each other in steps or continuously.

- The rigidifying elements 24 ensure that the heavy anode is held by the anode bar unit without any permanent deformation.

The electrolytic cell shown in the figures is intended for unidirectional current feed, i.e., the ascending bars are connected merely to one end of the current-conducting bars or bus bars disposed above the anodes. The rigidifying elements 24 of the current-conducting units are longer at their ends opposite the current feed end of the bus bars 1. A drive motor support bracket 27 is mounted on these projecting rigidifying elements on the ends thereof opposite the current supply ends of the anodes. The drive motor 56, the reduction gearing 57, and the drive sprockets are provided on the support bracket 27. As seen in FIGS. 1 and 2, the rotary motion of the drive motor 56 is decelerated by the reduction gearing 57, and the rotary motion of the latter is transmitted to the worms 16 by the chains 58. The worms 16 turn the worm gears 15, the axes of which are at right angles to the axes of the worms, and the coaxial threaded sleeves 14 are attached to the worm gears. The threaded sleeves 14 rotate in the bearing housing attached to the support bracket 27, but do not execute any axial movement. Threaded spindle 13 in sleeves 14 are thus forced to execute a linear motion.

One end of a wire cable 18 is attached to the end of each threaded spindle 13. The other end of the wire cable 18 is attached to the anode support unit 6 by suspension control means 35 in the form of threaded members that move vertically relative to anode support 6 upon the rotation of nuts encompassing the threaded members. The horizontally disposed wire cable 18, attached to the threaded spindle 13, passes under pulleys 17 carried by the anode assembly and thus supports the anode assembly.

The cell illustrated in FIGS. 1 and 2 comprises an anode mover having a drive motor 56 and, driven thereby, two motion changing assemblies, four wire cables 18 and, accordingly, four pulleys 17. The anode mover illustrated in FIGS. and 6, however, comprises the drive motor 56 and only a single motion converter. 'In this case, three wire cables are secured to the end of the threaded spindle 13, one of which cables is attached to the anode support 6 by a pulley 17, and the remaining two cables of which are attached to the anode support 6 about guide rollers 60 and pulleys 17. In this manner, the anode is suspended at three points.

In the cell shown in FIGS. 1 and 2, the pulleys 17 are disposed between the rigfiidifying elements 24, and their axles are supported therein.

The stationary anode sheath in the form of an insulating casing construction is mounted on the anode support 6 and is vertically adjustably suspended therefrom by means of others of the above-described control means 35 and comprises a rigid inner jacket 10, an inner profiled steel frame 40, a gas baflle 37, an outer jacket 38, an external steel frame 39, and a lower protective strip 53.

The upper portion of the sheath widens in the downward direction, while the lower portion of the sheath narrows in the downward direction. The space with the stationary sheath may be filled with fire brick, alumina, magnesia, calcium oxide, calcium fluoride, cryolite, burnt-out electrolytic carbon slag, coke dust, rock wool, glass wool, kieselguhr, perlite or mixtures thereof, or other high temperature insulating material, or may be empty.

A movable aluminum sheath 19 surrounds and moves downward with the carbonaceous anode mass during operation and is disposed within and spaced inwardly of the inner steel jacket 10. The lower portion of sheath 19 melts into the electrolyte, or is dissolved therein. Its upper portion is in contact with the anode mass which latter is still in the plastic condition. In correspondence with the amount of wear on the movable sheath 19, the latter must be constantly replenished at the upper portion. Elements 51 are formed along the inner surface of the movable sheath, and these embed themselves in the carbonaceous anode mass and prevent the detachment of the moving sheath 19 therefrom, and/or prevent the sheath from collapsing.

A loose layer 43 of alumina, magnesia, calicum oxide, calcium fluoride, cryolite, burnt-out electrolytic carbon slag, coke dust, rock wool, glass wool, kieselguhr, perlite, or mixtures thereof is maintained between the inner jacket 10 and the movable sheath 19, of a thickness of 1-20 mm., which layer ensures that the moving sheath 19 does not adhere to the rigid inner jacket 10. The material of the loose layer 43 is fed into a throat 59 formed on the upper portion of the fixed outer sheath, whence the alumina, due to the downward movement of the moving sheath, is continuously fed between the rigid inner jacket 10 and the moving sheath 19. At the lower end of the rigid inner jacket 10, expansion joints 46 between the inner frame T-sections 40 prevent the lower end of the jacket from becoming wavy due to the temperature difference between the upper and lower portions of the jacket during operation.

The protective strip 53 is formed at the lower portion of the outer sheath along the lower portion of the outer jacket 38, which strip can be replaced during operation and serves for absorbing the mechanical impacts of the conventional crust-breaking machine (not shown).

The lower portion of the outer or stationary sheath, i.e. the protective strip 53, the lower portion of the outer jacket 38, the gas bafile 37 and the lower portion of the inner rigid jacket 10, is made of heat-resistant steel plate.

For the removal of the anode bar assembly, a portable temporary anode support is provided, which is disposed above the'rows of anodes 54 and rests on the anode supports 6. As can be seen from FIG. 1, the temporary anode support comprises supporting beams 7 and hangers 8 longitudinally movable on beams 7 by means of supportmg rollers 9. The temporary anode support preferably comprises two supporting beams 7 and, on the latter, at least three, and preferably four hangers 8 are disposed.

The cells of the invention preferably also have the features recited below:

The radius of curvature of the current transfer surfaces 2 of the bus bars 1 amounts to 0.025-0.150 m., preferably 0.040.l0 m.

The central angle formed by the planes extending through the diametrically opposite edges of the contact surfaces 3 is 15-90, preferably 50-70, and the radius of the contact surfaces 3 is 0.024-0.149 m., preferably 0.039;0.099 m.

The height of the contact surfaces 3 of the anode is 0.5-1.0 m., preferably O.8-O.9 m., whereas the full height of the anode is 1.52.0 m., preferably 1.7-1.9 m., and one or more holes 23 or bolts or the like are arranged on the upper end of the anode, preferably symmetrical with respect to the axis of the anode and suitable for engagement by brackets 8 to support the anode assembly.

The elements 4 and/or the clamping bolts are made of an elastically deformable material, preferably spring steel; and/or the elements 4 and the clamping bolts 5 and the bus bars 1 adjoin each other with the interposition of an elastic element.

The anode ends are advantageously disposed at three heights of different levels in such a manner that'any three adjacent anodes are at different levels or heights.

The advantages of the cell constructed in accordance with the invention can be summarized as follows:

In the electrolytic cell constructed in accordance with the invention, it is possible to manufacture the aluminum, as compared to the conventional cell types, with a consumptionof electrical energy which is smaller by and/or the amperage, with an identical given cell surface, can be increased by 1020%, or the aluminum production can be increased to this extent. The investment cost,s, as well as the labor involved in operating the anode are substantially smaller in the cell of this invention. A more extensive mechanization of the operating processes, such as, for example, the pulling of the anodes, the feeding of the anode mass, the displacement of the anode bars, is made possible. The invention promotes to a consider able extent, and creates several decisive conditions in favor of, the further economical dimensional enlargement of the aluminum electrolysis cells.

In the cell of this invention, the pulling, of the anodes and the replacement of the anode bars may be executed as follows:

When pulling the anodes, the connection between the current-conducting bar or bus bar 1 and the contact surface 3 is interrupted by rotating the anodes about their axes; then, the anode is pulled out according to the generally known method.

The insert anodes, the reverse procedure is followed. Of course, the elements 4 and bolts 5 will be tightened and loosened as necessary, during removal or replacement of the anodes.

In view of the foregoing disclosure, therefore, it will be evident that all of the initially recited objects of the present invention have been achieved.

Although the present invention has been described and illustrated in connection with preferred embodiments, it is to be understood that modifications and variations'may be resorted to without departing from the scope of the invention, as those skilled in this art will readily understand.

Having described our invention, we claim:

1. An electrolytic cell for the production of aluminum, comprising a plurality of vertically disposed anodes and means suspending the anodes above a molten bath of electrolyte, the anodes having stubs comprised by flattened upper ends whose greatest width is greater than the greatest width of the lower portions of the anodes and whose thickness in a direction perpendicular to the direction of their greatest width is less than the thickness of the lower portions of the anodes, said supporting means comprising means for releasably gripping said upper ends of the anodes so as to apply a gripping action on said upper ends in the direction of said greatest width, and means for supplying electric current to said anodes through said upper ends, said upper ends of said anodes being rotatable upon release of said releasably gripping means while at the same level that is occupied by the upper ends when gripped.

2. A cell as claimed in claim 1, said upper ends of said anodes having relatively narrow side surfaces by which said upper ends are gripped, said relatively narrow surfaces comprising portions of the surface of a single vertically disposed cylinder.

3. A cell as claimed in claim 2, said current supplying means having a concave cylindrical surface congruent and in contact with a said cylindrical surface of said upper end.

.4. A cell as claimed in claim 3, the radius of said cylindrical surfaces being 0.025 to 0.150 m.

S. A cell as claimed in claim 4, said radius being 0.04 to 0.10 m.

6. A cell as claimed in claim 1, the side surfaces of said upper ends by which said upper ends are gripped being symmetrical on opposite sides of the axes of the anodes.

7. cell as claimed in claim 6, each of said side surfaces subtending an angle about the associated said axis of 15 to 90 of arc.

8. A cell as claimed in claim 7, said angle being 50 to of arc.

9. A cell as claimed in claim 1, said anodes below said upper ends tapering downwardly to lesser diameters adjacent their lower ends.

10. A cell as claimed in claim 1, said current supplying means comprising a bus bar, said anodes being disposed in a series along said bus bar, said gripping means comprising elements disposed on the side of each anode upper end opposite the bus bar and clamping bolts transverse to the bus bar and each interconnecting the ends of two said elements on opposite sides of the bus bar.

11. A cell as claimed in claim 10, said clamping bolts interconnecting said elements with play.

12. A cell as claimed in claim 10, said clamping bolts passing through holes through said bus bar.

References Cited UNITED STATES PATENTS JOHN H. MACK, Primary Examiner D. R. VALENTINE, Assistant Examiner U.S. Cl. X.R. 

